This invention relates to stereo systems in general and in particular to stereo speaker systems which permit a plurality of stereo speakers pairs to be coupled to a single amplifier output.
Stereo speaker systems which incorporate multiple pairs of stereo speakers are well known in the art. Many known stereo amplifiers provide multiple power outputs for coupling up to two pairs of speakers to the amplifier; however, the desire of the American consumer to utilize a greater number of speaker pairs has generally been thwarted by such known systems and has resulted in various unacceptable known techniques for coupling additional speaker pairs to an amplifier designed to drive one or two pairs of speakers.
A major problem associated with the coupling of additional pairs of speakers to known amplifier systems has been the failure of such known approaches to provide a proper impedance match between the amplifier output and the resultant speaker load. Those ordinarily skilled in the electrical art will appreciate that a typical stereo speaker has an impedance of eight ohms and that two such speakers coupled together will have an impedance of sixteen ohms when coupled in series and four ohms when coupled in parallel. This variation in load impedance from the output impedance of the amplifier results in power losses between the amplifier and the load and an unacceptable system.
Certain crude mechanical switching systems are known in the art which will compensate for this impedance by mechanically coupling an impedance matching device into the circuit between the speaker and the amplifier; however, these mechanical devices are generally unreliable and subject to unacceptable variations which result in noticeable power losses.
Additionally, such known switching systems can result in damage to speaker systems where the switch is located between the speaker system and the amplifier. An operator may inadvertently turn the output of the amplifier quite high while forgetting that the switch is in a non-select position. The subsequent selecting of a particular speaker pair can then result in the sudden and sometimes disastrous application of large amounts of power to a single speaker pair.